Various forms of sound barriers utilizing Helmholtz resonating chambers have been heretofore provided, but for various reasons these chambers have been mounted relative to each other in a manner to provide spacing slots therebetween extending through the barrier or the Helmholtz chambers have been mounted on backing panels in spaced parallel relationship relative to each other and with the backing panel including "breathing slots" formed therethrough in registry with the spacing between adjacent Helmholtz chambers. In the first instance, the slots are utilized to render the barrier at least somewhat visually transparent when the barrier is used along a roadway and, in the second instance, the breathing slots are provided to permit air circulation and to also render the barrier somewhat optically transparent. Examples of these two forms of Helmholtz chamber utilizing sound barriers are disclosed U.S. Pat. Nos.: 3,812,931 and 3,783,968. In addition, other sound barriers of somewhat similar construction are disclosed in U.S. Pat. Nos.: 3,630,310, 3,656,576, and 3,382,947.
It was previously believed that limited dimensional slots defined through a sound barrier utilizing Helmholtz chambers did not appreciably reduce the noise attenuation performance of the barrier and were desirable in order to provide a meaasure of visual transparency to the barrier and to minimize a reduction in noise attenuation performance of the barrier due to wind currents incident thereon. More recent studies indicate that the utilization of sound barrier structure provided with Helmholtz chambers and incorporating slots of the above-mentioned type results in appreciable reduction in noise attenuation performance of the barrier.
In addition, most sound barriers utilizing Helmholtz chambers must be reengineered in order to vary the resonance frequency of the barrier in order to adapt it for use in a particular noise abatement environment. Accordingly, a need exists for a sound barrier incorporating Helmholtz chambers and which does not include "breathing slots" or openings and which may be economically produced and "tuned" to a particular resonance frequency whereby the barrier may be specifically adapted for a particular noise abatement situation.